Influence of Physico-Chemical Parameters on Fish Distribution: A Case Study of Two Reservoirs in Tonk District, Rajasthan

Abstract

The present study investigates the influence of physico-chemical parameters on fish distribution and diversity in two major reservoirs of Tonk District, Rajasthan  Bisalpur Dam and Isarda Dam, both located on the Banas River. A total of 25 fish species were recorded from Bisalpur Dam and 18 from Isarda Dam, belonging to families Cyprinidae, Channidae, Siluridae, Cichlidae, Schilbeidae, Notopteridae, Belonidae, Bagridae, and Poeciliidae. Monthly sampling was conducted over a period of 12 months using cast nets, drag nets, and hand nets. Physico-chemical parameters including water temperature, pH, dissolved oxygen (DO), turbidity, total dissolved solids (TDS), total suspended solids (TSS), biochemical oxygen demand (BOD), chemical oxygen demand (COD), total alkalinity, and total hardness were measured following standard APHA methods. Results revealed that Bisalpur Dam exhibited significantly better water quality with higher DO (6.8–7.8 mg/L), lower turbidity (16–24 NTU), and near-neutral pH (7.1–7.5), which supported a richer and more diverse fish assemblage dominated by Indian Major Carps. Isarda Dam showed comparatively lower water quality due to higher siltation, turbidity (28–40 NTU), and lower DO (5.6–6.4 mg/L), resulting in dominance of hardy species like snakeheads and catfishes. Shannon-Wiener diversity index (H') and Simpson's index were calculated for both sites. The study concludes that physico-chemical gradients are primary determinants of fish community structure in these reservoirs, and that improved water resource management is essential for sustaining freshwater fish biodiversity in Tonk District.